Method Of Manufacturing A Plate-Type Heat Exchanger Using A Set Of Spacer Blocks

ABSTRACT

A method of manufacturing a plate heat exchanger of the type comprising a plurality of plates defining paths for fluids to flow through, the plates being assembled to each other by brazing, and a heat exchanger produced by such a method is presented.

The present invention relates to a method of manufacturing a plate heatexchanger of the type comprising a plurality of plates defining pathsfor fluids to flow through, the plates being assembled to each other bybrazing, and a heat exchanger produced by such a method.

Plate heat exchangers usually consist of a stack of plates definingpassages for fluids.

In order to improve the heat exchange between the fluids, corrugatedsheets, known as heat exchange fins, may be sandwiched between saidplates that form the heat exchanger. The resulting passages are closedat the sides by side bars. Having been put together in this way, theheat exchanger is then brazed to make the assembly rigid and ensurebetter thermal contact.

Plate heat exchangers can be made of aluminum or an aluminum alloy forgood thermal conductivity and good mechanical integrity.

Prior art heat exchangers, as described for example in FR-A-2 815 895,are capable of exchanging heat from many fluids, for example more than 5fluids. The heat exchange fins, which are usually used, have both athermal function of increasing heat exchange surface area and improvingthe thermal efficiency of the exchanger, and a mechanical function ofmaintaining the mechanical integrity of the heat exchanger during thebrazing and preventing buckling of the passages. Thus it can happen thatmechanical integrity is the determining aspect of the assembly. Inparticular, the fin is then no longer optimized thermally.

It is therefore known practice to replace said heat exchange fins withan improved coating on the separating plates. In some cases it can alsobe helpful to reduce the density of the fin, or even remove itcompletely to avoid masking the improved surface area of the plate withsaid fin.

It would therefore be advantageous to develop a method for producing aheat exchanger that makes it possible to maintain the mechanicalintegrity of said exchanger during the brazing step and that is easy toimplement.

It is an object of the present invention to provide such a method ofmanufacture.

The invention provides a method of manufacturing a plate heat exchangerof the type comprising a plurality of plates which, together with sidebars arranged on the plates, define paths for fluids to flow through,comprises at least the following successive steps:

-   -   a stack of a plurality of plates separated by side bars is        provided,    -   at least one removable set of spacer blocks consisting of at        least two spacer blocks, connected together by at least one        connecting element, is introduced between plates of said heat        exchanger,    -   said heat exchanger is brazed, and    -   the removable set of spacer blocks is removed        said method being characterized in that the connecting element        is shaped in such a way as to allow a rotary movement of the set        of spacer blocks about the main axis of each of said spacer        blocks, each spacer block having an essentially constant cross        section along its main axis, and in that after the introduction        step, a rotary movement is applied to all the spacer blocks of        said set about their main axes, in such a way as to press each        spacer block against said plates;        after the brazing step, a rotary movement is applied to all the        spacer blocks of said set about their main axes, in such a way        as to release said spacer blocks and in which said removable set        of spacer blocks is selected in such a way that either

i)

-   -   said cross section is essentially polygonal in shape, and    -   the length of at least one of the main diagonals of said cross        section is greater than or equal to the distance between the        plates of the heat exchanger between which said spacer block is        intended to be introduced;    -    or

ii)

-   -   said cross section is essentially elliptical in shape, and    -   the length of the major axis of said cross section is greater        than or equal to the distance between the plates of the heat        exchanger between which said spacer block is intended to be        introduced.

Advantageously, the method according to the invention makes it possibleto introduce and remove a plurality of spacer blocks between the platesof the heat exchanger easily and quickly.

As a consequence, the removable set of spacer blocks is withdrawn afterthe brazing step, thus freeing up space in the fluid flow path.

Introducing a removable set of spacer blocks connected together by aconnecting element simplifies the method, as it can be tedious workintroducing and later removing the spacer blocks individually.

In addition, there is no need when carrying out a method according tothe invention to position the spacer blocks while the plates of theexchanger are being stacked, because the spacer blocks can be introducedat a later stage.

A method according to the invention may also include one or more of theoptional features set out below, taken individually or in all possiblecombinations:

-   -   a plurality of removable sets of spacer blocks, which are fixed        together by fixing means, are introduced;    -   a single removable set of spacer blocks is introduced between        two plates of said heat exchanger;    -   the method includes a step in which at least one removable set        of spacer blocks is selected, in which the connecting element is        shaped in such a way as to allow a rotary movement of the set of        spacer blocks about the main axis of each of said spacer blocks;    -   said removable set of spacer blocks is selected in such a way        that:        -   each spacer block has an essentially constant cross section            along its main axis,        -   said section being essentially polygonal in shape, and        -   the length of at least one of the main diagonals of said            cross section is greater than or equal to the distance            between the plates of the heat exchanger between which said            spacer block is intended to be introduced;    -    after the introduction step, a rotary movement is applied to        all the spacer blocks of said set about their main axes, in such        a way as to press each spacer block against said plates;    -    after the brazing step, a rotary movement is applied to all the        spacer blocks of said set about their main axes, in such a way        as to release said spacer blocks;    -   said removable set of spacer blocks is selected in such a way        that:        -   each spacer block having a cross section essentially            constant along its main axis,        -   said section being essentially elliptical in shape, and        -   the length of the major axis of said cross section being            greater than or equal to the distance between the heat            exchanger plates between which said spacer block is intended            to be introduced,    -    after the introduction step, a rotary movement is applied to        all the spacer blocks of said set about their main axes, in such        a way as to press each spacer block against said plates;    -    after the brazing step, a rotary movement is applied to all the        spacer blocks of said set about their main axes, so as to        release said spacer blocks;    -   the spacer blocks of said set of spacer blocks and the        connecting elements that are selected are made of one or more        materials whose melting point is 700° C. or above, preferably        900° C. or above (such as stainless steel);    -   all the spacer blocks of said set have their main axes        approximately parallel to each other.

The invention also relates to a plate-type heat exchanger of the typecomprising a plurality of plates made of a brazable material, whichexchanger is noteworthy in that it can be produced by the methodaccording to the invention.

For the purposes of the invention, “removable set of spacer blocks”means a set of spacer blocks which, after the step of brazing theexchanger, can be removed and reused without requiring structuralmodification.

The invention consists in using a removable set of spacer blocks tomechanically support the heat exchanger during the brazing step. Thereason for this is that, in order to improve the brazing step, it isknown practice to apply pressure to the heat exchanger during saidbrazing step. The set of spacer blocks ensures that the plates formingthe heat exchanger do not buckle under the pressure.

The use of a set of spacer blocks reduces the number of operations to becarried out during manufacture of the heat exchanger.

In a first embodiment of the invention, the method also includes a stepin which the removable set of spacer blocks is selected in such a waythat each spacer block is of essentially constant cross section alongits main axis:

-   -   said cross section being square in shape, and    -   the length of the side of the square being equal to the distance        between the heat exchanger plates between which said spacer        block is intended to be introduced.

The spacer blocks of the selected set are connected together, forexample by means of connecting bars distributed at regular intervalsalong the spacer blocks of the set. The connecting bars may be welded tothe spacer blocks.

Advantageously, such a set is easy to use and makes it very easy toarrange a plurality of spacer blocks between two plates of the heatexchanger, since all that is required is to slide the set of spacerblocks between the plates of the exchanger.

After the brazing step, the set of spacer blocks can easily be removed,and this operation again is made easy by the connecting elements.

In one embodiment of the invention, the method also includes a step inwhich the removable set of spacer blocks is selected in such a way that:

-   -   each spacer block has an essentially constant cross section        along its main axis,    -   said cross section being lozenge-shaped,    -   the length of the long diagonal of said cross section is greater        than or equal to the distance between the heat exchanger plates        between which said spacer block is intended to be introduced,        and    -   the length of the short diagonal of said cross section is less        than the distance between the heat exchanger plates between        which said spacer block is intended to be introduced.

The word “lozenge” is used to mean any simple polygon with fourequilateral sides.

The connection between the spacer blocks can be provided by connectingelements, connected to the spacer blocks, by welding for example.

The connecting elements may comprise a mechanical device such as ahinge, spring, drive, or rod that makes it possible to apply to all thespacer blocks a movement, e.g. a rotary movement about the main axis ofeach of the spacer blocks of the set of spacer blocks.

Advantageously, the selection of such a removable set of spacer blocksmakes it possible to position the set of spacer blocks between at leasttwo plates of the heat exchanger in such a way that the contact area ofeach of the spacer blocks with the plates is less than or equal to 15%of the total surface area of each spacer block, preferably less than orequal to 5% of the total surface area of each spacer block.

The smaller the contact area between each spacer block and the platesbetween which the spacer blocks are introduced, the less the risk thatthe spacer blocks will be welded to said plates during the brazing step.In this embodiment, the selected set of spacer blocks is positionedbetween the plates of a pre-assembled heat exchanger.

This step of putting the spacer blocks in position may comprise twosub-steps. In the first, each set of spacer blocks may be introducedbetween two plates with an orientation such that the long diagonal ofthe cross section of each spacer block lies in a plane approximatelyparallel to the plane defined by the plates.

Advantageously, since the set of spacer blocks has been selected in sucha way that the short diagonal of the cross section of each spacer blockhas a length less than or equal to the distance between the plates ofthe heat exchanger between which the set of spacer blocks is intended tobe introduced, each spacer block can be introduced without difficultybetween the two plates.

In the second sub-step, once the set of spacer blocks has beenintroduced between the two plates of the exchanger, a movement can beapplied, by means of the connecting element, to all of the spacerblocks, causing each spacer block to pivot about its main axis so thateach spacer block is pushing against the two plates.

Advantageously, in this position, the set of spacer blocks maintainsgood mechanical integrity of the heat exchanger during the brazing step.

Also in this embodiment, the method includes a step after the brazingstep in which the removable set of spacer blocks is removed from betweenthe plates of the brazed heat exchanger.

Advantageously, the spacer blocks of the removable set of selectedspacer blocks are not welded to the plates in the course of the brazingstep, owing among other things to the fact that the contact area betweeneach of the spacer blocks and the plates is small.

In this embodiment, the removable set of spacer blocks can be removed bypivoting each spacer block about its main axis in such a way as toorient it such that the long diagonal of its cross section is in a planeapproximately parallel to the plates. All the spacer blocks forming theset of spacer blocks can be pivoted at the same time by means of theconnecting element.

Advantageously, this simplifies the step of removing the spacer blocks.

In another embodiment of the invention, the method also includes a step,the removable set of spacer blocks is selected therefrom in such a waythat:

-   -   1) each spacer block is of essentially constant cross section        along its main axis,    -   2) said cross section is in the shape of an ellipse,    -   3) the length of the major axis of said cross section is greater        than or equal to the distance between the heat exchanger plates        between which said set of spacer blocks is intended to be        introduced, and    -   4) the length of the minor axis of said cross section is less        than or equal to the distance between the heat exchange plates        between which said removable set of spacer blocks is intended to        be introduced.

Spacer blocks for the selected removable set of spacer blocks areconnected to each other by a connecting element, such as a rigid barwelded to each spacer block, or a bar connected to each spacer block bymeans of a mechanical device such as a hinge, spring, drive or rod, thatallows a rotary movement to be applied to each spacer block of theremoval set of spacer blocks about their main axes. Selecting such a setof spacer blocks has advantages similar to the previous embodiment.

In particular, the contact area of each spacer block, once positionedbetween the plates, can be less than or equal to 15% of the totalsurface area of said spacer block, preferably less than or equal to 5%of the total surface area of said spacer block.

The spacer blocks of the removable sets of spacer blocks selected duringa method according to the invention are preferably made of one or morematerials whose melting point is above the brazing temperature, forexample 900° C. or above, or 1500° C. or above. The spacer blocks of thesets of selected spacer blocks may for example be made of stainlesssteel.

A method according to the invention can also include a step in whicheach spacer block of the selected sets of spacer blocks is covered witha product that prevents or limits brazing during the brazing phase, suchas STOP OFF®.

Advantageously, the use of such a product eases the step of removing thesets of spacer blocks of cross sections that differ from the embodimentsdescribed, such as hexagonal cross sections according to the invention.

The invention is not limited to the embodiment described and can beinterpreted non-restrictively so as to encompass any equivalentembodiment.

In particular, the invention is applicable to any type of plate-typeheat exchanger assembled by brazing. In particular, the method accordingto the invention can be carried out with sets of spacer blocks in whichthe spacer blocks have cross sections different from the embodimentsdescribed, such as hexagonal cross sections.

1-6. (canceled)
 7. A method of manufacturing a plate heat exchanger ofthe type comprising a plurality of plates which, together with side barsarranged on the plates, define paths for fluids to flow through,comprising at least the following successive steps: providing a stack ofa plurality of plates separated by side bars, introducing at least oneremovable set of spacer blocks consisting of at least two spacer blocks,connected together by at least one connecting element, between plates ofsaid heat exchanger, wherein the connecting element is shaped in such away as to allow a rotary movement of the set of spacer blocks about themain axis of each of said spacer blocks, each spacer block having anessentially constant cross section along its main axis; brazing saidheat exchanger, and removing the removable set of spacer; applying arotary movement to all the spacer blocks of said set about their mainaxes, in such as away as to press each spacer block against said plates,after the introduction step; applying a rotary movement to all thespacer blocks of said set about their main axes, in such a way as torelease said spacer blocks, after the brazing step, wherein; removableset of spacer blocks is selected in such a way that either i) said crosssection is essentially polygonal in shape, and the length of at leastone of the main diagonals of said cross section is greater than or equalto the distance between the plates of the heat exchanger between whichsaid spacer block is intended to be introduced; or ii) said crosssection is essentially elliptical in shape, and the length of the majoraxis of said cross section is greater than or equal to the distancebetween the plates of the heat exchanger between which said spacer blockis intended to be introduced.
 8. The method of claim 7, wherein aplurality of removable sets of spacer blocks, which are fixed togetherby fixing means, are introduced.
 9. The method of claim 8, wherein asingle removable set of spacer blocks is introduced between two platesof said heat exchanger.
 10. The method of claim 7, wherein the spacerblocks of said set of spacer blocks and the connecting elements that areselected are made of one or more materials whose melting point is 700°C. or above.
 11. The method of claim 7, wherein the spacer blocks ofsaid set of spacer blocks and the connecting elements that are selectedare made of one or more materials whose melting point is 900° C. orabove.
 12. The method of claim 11, wherein said material is stainlesssteel.
 13. The method of claim 7, wherein all the spacer blocks of saidset have their main axes approximately parallel to each other.
 14. Aplate-type heat exchanger of the type comprising a plurality of platesmade of a brazable material, which exchanger is characterized in that itcan be produced by the method according to claim 7.